<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
<div id="main" class="container">
    <p>这是一个段落</p>
</div>
<style>
    /* 3个css规则  role*/
    css roul 
    css  java
    h1{
        color: blue ;

    }
    /* 最后的元素 */
    .container p{
        color: red;
    }
    #main p{
        color: green;
    }
</style>  
</body>
</html>